16 oz claw hammer: fibreglass handle, 16 oz head, 0.70 kg.
2
From how high
m
49 ft. Measured to the deck or ground below, as DROPS measures it: not to the top of someone's head.
3
Below the work
Worker below wears a hard hat
Barricade the drop zone at
On the way down
Loading the 3D view…
Lands with
103 J
Fatality
Following the claw hammer
Straight below the workBarricaded drop zone
4
The answer
Could kill whoever is below
On the DROPS Calculator’s curves this reaches the fatal band, even for someone wearing a hard hat.
Time to fall
1.75s
less time than it takes to hear a shout and move
Speed when it lands
62km/h
17.2 m/s
Energy
103J
1.9× a hard hat's 54.5 J top impact test
Average force
4.1kN
if stopped in 25 mm; a hard hat may pass under 4.45 kN in its test
A ricochet can land 7.6 m past the barricade
Falling clear, it lands below the work. But if it strikes round steel on the way (a pipe, scaffold tube or handrail), it can be thrown up to 15.1 m out, against a drop zone of 7.5 m (1 m per 2 m up).
How big a drop zone, for 15.0 m
1 m out for every 3 m up
5.0 m
1 m out for every 2 m up
7.5 m
A strike on round steel: furthest it lands (restitution 0.66)
15.1 m
With no energy lost, up to twice the fall (Energy Safety Canada)
30.0 m
No Canadian or US regulation sets a distance: the law says to keep people out of the area things can fall into. The first two are rules of thumb in published contractor and university procedures. The third is this tool's physics: a strike on a round steel tube with a restitution of 0.66, the figure Energy Safety Canada's draft exclusion zone tool uses for steel on steel. Real objects tumble, and can go further.
Likely outcome by mass and height, hard hat worn
Slight: first aidMinor: medical treatmentMajor: lost timeFatality
Stop it falling, then keep people out from under it
1Take the hazard away. Keep tools and materials back from open edges, do the work at grade where you can, and bring nothing aloft that the job doesn’t need.
2Tether and contain. Tie tools to the worker or the structure with attachments and tethers rated for the tool (ANSI/ISEA 121), and carry small parts in closed bags or buckets, not pockets.
3Catch it at the edge. Toe boards, screens or mesh where material is stacked, debris nets, catch platforms and covered walkways under the work.
4Keep people out from under it. Barricade the drop zone on every side and approach, sign it, and have one person control who goes in. Size it for a ricochet, not just a straight drop.
5Protect the head that is left. Hard hats for everyone on site, Type 2 (CSA) or Type II (ANSI) where an object could strike from the side, with chin straps where a hat could come off. A hard hat is tested to about 54.5 J; it is the last line, not the plan.
The rules · Alberta
Workers in a work area where there may be falling objects must be protected by an overhead safeguard able to take the shock load. Where workers enter only now and then, warning signs, horns or flashing lights may do instead.
Toe boards at least 140 mm high (gap under 6 mm) where material could fall more than 1.8 m from a permanent surface, or 3.5 m from a temporary scaffold or platform.
Safety nets to ANSI A10.11, reaching at least 2.4 m beyond the work and no more than 6 m below it.
Industrial headwear to CSA Z94.1-15 or ANSI Z89.1. No loads over workers where reasonably practicable, and nobody under a suspended load. Nobody enters an area where a chute drops or throws material.
No distance is set for the barricaded area below the work: it is whatever keeps workers out of reach of what can fall.
A summary to plan with. The regulation and your employer's procedures govern.
Standards and guidance
DROPS Calculator. The industry’s chart of likely outcome by mass and fall height, fitted to skull-fracture data, assuming a hard hat is worn and the fall measured to the deck or ground below. The bands here are its curves.
ANSI/ISEA Z89.1. Type I hard hats are tested on top with a 3.6 kg striker at 5.5 m/s (54.5 J) and must let less than 4,450 N through; Type II hats are also tested off the top (2014 edition figures; a 2026 edition adds optional tests). In NIOSH testing of one Type I model, the hat failed above about 63 J.
CSA Z94.1-15. Industrial protective headwear: Type 1 protects the crown, Type 2 the crown, sides and back. Most Canadian jurisdictions require it, or ANSI Z89.1, on site.
ANSI/ISEA 121-2023. Dropped object prevention solutions: anchor attachments, tool attachments, tool tethers and containers, each rated for a capacity and drop tested (a tether at twice its rated load over twice its length). Voluntary; it doesn’t say which tools must be tethered.
Energy Safety Canada. Dropped Objects Prevention best practice: anchor tools under about 2 kg to the worker, and size exclusion zones for deflection, which with no energy lost “can be up to twice the distance that an object falls.”
OSHA. 29 CFR 1926.501(c) and 1910.28(c): where workers are exposed to falling objects, hard hats plus toe boards, screens or guardrails, a canopy, or a barricaded area nobody may enter. 1926.759: secure tools and materials aloft in steel erection, and no other work below without overhead protection.
Outcome bands: the DROPS Calculator's curves (dropsonline.org), with credit. TruStar Safety isn't affiliated with DROPS, and DROPS doesn't endorse this tool.
Pick a tool and a height, and watch it fall in 3D onto the hard hat of a worker below, or strike a steel pipe on the way down and be thrown out past the barricade. The calculator shows how fast it lands, the energy it hits with against what a hard hat is tested to take, the likely outcome on the DROPS Calculator's curves, how far a ricochet can carry it, and the rules for your province or territory.
How hard a dropped tool hits
A dropped object's energy grows with the height it falls: mass times gravity times height. A 0.7 kg claw hammer knocked off a deck 15 m up lands 1.75 seconds later at about 62 km/h, carrying 103 J, nearly twice the 54.5 J a hard hat's top is tested with. Nobody below hears a shout and moves in that time.
Slight. First aid at most, for someone wearing a hard hat.
Minor. An injury needing medical treatment.
Major. A lost time injury.
Fatality. On the DROPS curves, a 0.7 kg hammer reaches this from about 14.7 m, a 1 kg shackle from about 10 m.
Why a drop zone needs room for a ricochet
Falling clear, a tool lands below the work. Striking a pipe, a scaffold tube or a handrail on the way down, it can be thrown sideways: a strike on round steel can carry it about as far out as it fell, and Energy Safety Canada notes that with no energy lost a deflection can reach twice the fall. Rules of thumb of 1 m out for every 2 or 3 m of height don't cover that. Size the barricade for what the object could strike, and spend the effort on stopping it falling.
Stop it falling
Tether tools with anchor attachments, tool attachments and tethers rated for the tool (ANSI/ISEA 121), and carry small parts in closed bags or buckets.
Toe boards, screens and nets. Toe boards at the edge, screens or mesh where material is stacked, debris nets and catch platforms below.
Keep the edge clear. Store nothing near an open edge, and secure what isn't in use aloft.
Barricade and control the drop zone on every side and approach, with signs and one person controlling entry.
Hard hats for everyone, Type 2 (CSA) or Type II (ANSI) where an object could strike from the side, with chin straps where a hat could come off.
If something drops
Stop the work and keep everyone clear until the area is safe. Treat it as an incident whether it hit anyone or not: report it, find out why it fell and what was below, and fix the cause before work at height starts again.
Sources: the DROPS Calculator's outcome curves and its 40 joule rule (DROPS Recommended Practice and Dropped Object Consequence Calculator, 2021), used with credit; TruStar Safety isn't affiliated with DROPS, and DROPS doesn't endorse this tool. ANSI/ISEA Z89.1 hard hat test figures (2014 edition, from ISEA); CSA Z94.1-15; NIOSH, Wu et al. 2024; ANSI/ISEA 121-2023; Energy Safety Canada, Dropped Objects Prevention best practice (2021); skull fracture energies from Yoganandan et al. 1995; OSHA 29 CFR 1926.501(c), 1926.451(h), 1926.759 and 1910.28(c); each province's and territory's OHS regulation and the federal COHS Regulations (sections in the rules panel). Masses are manufacturers' published weights for typical models. The ricochet is a strike on a round steel tube with a coefficient of restitution of 0.66, the figure Energy Safety Canada's draft exclusion zone tool uses for steel on steel; real objects tumble and can land further.
Frequently asked questions
How hard does a dropped tool hit?
Its energy when it lands is its mass times gravity times the height it falls (m·g·h). A 0.7 kg claw hammer dropped 15 m lands at about 62 km/h with 103 J, nearly twice the 54.5 J a hard hat’s top is tested with under ANSI/ISEA Z89.1. A 1 kg object from 10 m carries about 98 J. The force depends on how quickly it stops: the faster the stop, the higher the force.
Can a dropped hammer kill someone wearing a hard hat?
Yes. On the DROPS Calculator’s curves, which assume a hard hat and other standard PPE are worn, a 0.7 kg hammer reaches the fatal band from about 14.7 m, and a 1 kg object from about 10.5 m. A hard hat is designed to absorb some of the energy of a blow from small falling objects; it is the last line of defence, not the plan.
How big should a drop zone be?
No Canadian or US regulation sets a distance: the law requires the area things could fall into to be barricaded and kept clear, or protected overhead. Published contractor and university procedures use rules of thumb from 1 m out for every 3 m of height to 1 m for every 2 m. But a tool that strikes round steel on the way down can be thrown about as far out as it fell, and Energy Safety Canada notes that with no energy lost a deflection can reach twice the fall. Size the zone for what the object could hit, and stop it falling in the first place.
What does a hard hat protect against?
Under ANSI/ISEA Z89.1, a Type I hard hat’s top is tested with a 3.6 kg striker at 5.5 m/s (54.5 J), and must let less than 4,450 N through to the head. Type II hats are also tested for impacts off the top. CSA Z94.1 Type 1 hats protect the crown; Type 2 hats the crown, sides and back. In NIOSH testing of one Type I model, the hat failed above about 63 J.
What is ANSI/ISEA 121?
The American standard for dropped object prevention solutions (2018, revised 2023). It covers anchor attachments, tool attachments, tool tethers and containers, each rated for a capacity and drop tested. It is voluntary and doesn’t say which tools must be tethered; Canada has no CSA equivalent. Energy Safety Canada’s best practice advises anchoring tools under about 2 kg to the worker.
What is the DROPS Calculator?
A chart from DROPS, the industry’s Dropped Objects Prevention Scheme, that gives the likely outcome of a dropped object by its mass and the height it falls: slight (first aid), minor (medical treatment), major (lost time) or fatality. Its curves are fitted to skull-fracture data, assume a hard hat is worn, and measure the fall to the deck or ground below. This tool uses its curves, with credit.
